Humans have known and used stone as a building material since ancient times. Its unique aesthetic and physical qualities have made stone a desirable material in building and construction as well as in decorative art and sculpture.
Pavers are concrete blocks that are made by using a casting process, a pressing process, a compacting process, or a combination of vibration and pressing. Pavers are generally laid in interlocking pattern. These pavers are also sometime referred as paving stones. These pavers can be removed when damaged during service life with a new one reducing any service interruption. Interlocking pavers could be designed to have a gap between the patterns that provides for draining of water to sub layers.
ASTM C 936 provides criteria that concrete pavers need to satisfy but is not limited to the following: an average compressive strength of 8,000 psi; an average water absorption no greater than 5%; and resistance to at least 50 freeze-thaw cycles with average material loss not exceeding 1%. In addition to the ASTM requirements, one may also wish that the payers satisfy additional requirements, including reduced efflorescence (e.g., reduced leaching out of reaction product due to concentration gradients); good color retention; and abrasion resistance depending on where the pavers are being used.
Like pavers, blocks are also pre-cast concrete produced either by casting or pressing processes, or similar compacting processes. Blocks are also referred to as concrete masonry units (CMUs), hollow blocks and concrete blocks. When these blocks are made with fly ash they are called cinder blocks. These blocks generally have a hollow structure. Artificial or man-made paving stones and construction block materials have been studied in efforts to replace the expensive and scarce natural material with low-cost, readily produced mimics. Such efforts, however, have yet to produce in a synthetic material that possesses the desired appearance, texture, density, hardness, porosity and other aesthetics characteristic of stone while at the same can be manufactured in large quantities at low cost with minimal environmental impact.
Blocks are expected to provide better structural property compared to clay bricks (for load bearing masonry structure), and a smoother surface when producing a masonry wall. In addition, interlocking concrete masonry units do not require mortar to bind the units. Some blocks can be used to build a hollow structure that results in good sound and thermal insulation as compared to a solid structure.
Blocks have to generally comply with the requirements of ASTM C90, Standard Specification for Loadbearing Concrete Masonry Units. Blocks that comply with this standard are ensured to be acceptable as regards strength, geometry, durability and fire resistance, and are generally acceptable for use in standard commercial construction projects.
Most artificial stone mimics are prepared by blending natural stone powder and mineral particulate with Portland Cement. The natural stone, mineral and cement blend is mixed with water, formed into the desired shapes, and cured. This method suffers from a number of deficiencies, including poor reproducibility, low yield, deterioration, high finishing costs, unsatisfactory mechanical properties, and the like.
Other artificial stone mimics are prepared by blending natural stone powder and minerals with a synthetic resin (e.g., acrylic, unsaturated polyester, epoxy). These methods also suffer from a number of deficiencies, including poor reproducibility, low yield, deterioration, high finishing costs, unsatisfactory mechanical properties, and the like.
Furthermore, existing methods typically involve large energy consumption and carbon dioxide emission with unfavorable carbon footprint.
There is an on-going need for novel composite paving stones and construction block materials that exhibit good aesthetic and physical characteristics and can be mass-produced at low cost with improved energy consumption and desirable carbon footprint.